This invention relates to temperature control of boilers for hydronic heating systems equipped with tankless water heaters.
Typically, the operation of these boilers is controlled by a thermostat that turns the burner on when the boiler's internal temperature drops below a "LOW" value and turns it off when the temperature exceeds a "HIGH" value, thereby maintaining the temperature of the boiler at a constant average value.
These boilers also supply the domestic hot water and therefore have to be in operation even when no space heating is required. In the majority of cases residential use of hot water is limited to few short intervals during each 24 hour period, therefore maintaining the boiler at an elevated temperature around the clock will cause a significant standby heat loss during the warm seasons.
Since during the warm seasons the boiler can be turned off when no hot water demand is present, the standby, loss is some times reduced by using a programmable timer to turn the boiler off during the time periods when no hot water demand is anticipated.
As shown in FIG. 1, a programmable timer is programmed to turn switch 2 whenever hot water demand is anticipated and to keep it on for the expected duration of the demand. Switch 2 controls the power going to thermostat 3 and allows the burner of the boiler 4 to operate only for the duration of the programmed periods.
This method is simple and inexpensive, but has the disadvantage of requiring frequent reprogramming as the seasons change and the time during which the boiler has to provide space heat gradually increases or decreases. In addition, the accommodation of unscheduled hot water demands will also require temporary reprogramming or bypassing of the timer.
It is therefore the object of the invention to provide a controller for boilers that will minimize the standby heat loss and will automatically adjust the time periods during which the boiler is operated so both unscheduled hot water demands and seasons change are accommodate without reprogramming.